Optical fiber having a low polarization mode dispersion and process and apparatus for producing it
View Patent ↗An apparatus for producing a low-PMD optical fiber having a furnace for melting a lower portion of an optical preform; a traction device for pulling an optical fiber from the lower portion of an optical preform; a spinning device for imparting a substantially constant and unidirectional spin to the optical fiber as it is pulled, which causes the fiber to undergo an elastic torsion; a winding device for winding the optical fiber onto a reel; and a twisting device for imparting to the spun optical fiber a unidirectional twist in a direction opposite the elastic torsion, so as to control the residual twist in the optical fiber. A process for producing the fiber, an optical fiber and a cable are also provided.
1. A process for producing a low-PMD optical fiber, comprising:
drawing a glass preform into an optical fiber;
spinning the optical fiber unidirectionally about its axis during drawing, causing the optical fiber to undergo an elastic torsion;
winding the optical fiber onto a reel; and
twisting the spun optical fiber about its axis in a direction opposite the direction of said elastic torsion, for controlling said elastic torsion.
2. The process according to claim 1 , wherein twisting comprises imparting a twist to the optical fiber that is greater in module than said elastic torsion, so as to provide the optical fiber with a residual torsion.
3. The process according to claim 1 , wherein twisting the spun optical fiber is performed at a substantially constant rate.
4. The processing according to claim 2 , wherein the residual torsion is in module between 0 and about 1.5 turns/m.
5. The process according to claim 2 , wherein the residual torsion is in module between about 0.3 and 1 turn/m.
6. The process according to claim 1 , wherein spinning the optical fiber is performed at a substantially constant rate.
7. The process according to claim 1 , wherein spinning the optical fiber is performed at a variable rate.
8. The process according to claim 7 , wherein spinning the optical fiber is performed according to a spinning function obtained by superposing a constant function and a periodic function.
9. The process according to claim 1 , wherein spinning the optical fiber is performed at a rate between about 1 and 8 turns/m.
10. The process according to claim 1 , wherein twisting the optical fiber is performed while winding the optical fiber onto the reel.
11. The process according to claim 1 , further comprising the steps of unwinding the optical fiber from said reel and rewinding the optical fiber onto a further reel, wherein twisting to the optical fiber is performed while unwinding the optical fiber or while rewinding the optical fiber.
12. An apparatus for producing a low-PMD optical fiber, comprising:
a furnace for melting a lower portion of an optical preform;
a traction device for pulling an optical fiber from the lower portion of the optical preform;
a spinning device for imparting a unidirectional spin to the optical fiber about its axis as it is pulled, in such a way that the optical fiber undergoes an elastic torsion;
a winding device for winding the optical fiber onto a reel; and
a twisting device for imparting to the spun optical fiber a twist about its axis in a direction opposite said elastic torsion.
13. The apparatus of claim 12 , wherein the twisting device is associated to the winding device.
14. The apparatus of claim 12 , further comprising an unwinding device for unwinding the optical fiber from the reel, the twisting device being associated to the unwinding device.
15. The apparatus of claim 12 , further comprising at least a coating device for applying at least a protective coating to the optical fiber as it is pulled, the spinning device being positioned between the at least a coating device and the traction device.
16. An optical cable, comprising at least an optical fiber having a unidirectional intrinsic spin and an elastic twist that is substantially null or opposite said spin and greater than zero in module.
17. The optical cable of claim 16 , wherein said unidirectional intrinsic spin is substantially constant.
18. The optical cable of claim 16 , wherein the elastic twist is in module between 0 and about 1.5 turns/m.
19. The optical cable of claim 17 , wherein the elastic twist is in module between about 0.3 and 1 turn/m.
20. The optical cable of claim 16 , wherein the intrinsic spin is in module between about 1 and 8 turns/m.
21. An optical fiber having a unidirectional intrinsic spin and an elastic twist that is substantially null or opposite said spin and greater than zero in module.
22. The optical fiber of claim 21 , wherein the unidirectional intrinsic spin is substantially constant.
23. The optical fiber of claim 21 , wherein the elastic twist is in module between 0 and about 1.5 turns/m.
24. The optical fiber of claim 23 , wherein the elastic twist is in module between about 0.3 and 1 turn/m.
25. The optical fiber of claim 21 , wherein the intrinsic spin is in module between about 1 and 8 turns/m.